Microstructures and properties of glass fiber reinforced PTFE composite substrates with laminated construction

Abstract

Three kinds of composite substrates have been fabricated by stacking layers of glass fiber cloth (GFC) or glass fiber mat (GFM) impregnated with polytetrafluoroethylene (PTFE). The difference of the three kinds of substrates is the layered structures, composed of simplex GFC or GFM, or GFC and GFM alternately. The effects of glass fiber types and laminated constructions on the physical properties of composite substrates, such as dielectric constant (εr), dielectric loss (tgδ), water absorption, coefficient of thermal expansion (CTE) and microstructures were studied. The PTFE/GFM composites show similar performances with PTFE/GFC composites. The results demonstrate that the dielectric constant (GFM up to 2.23, GFC up to 2.24) and dielectric loss (GFM up to 0.0016, GFC up to 0.0018) are increased with an increase of the number of layers, on the contrary, the temperature coefficient of dielectric constant (τε) of composites has a decreasing tendency (GFM of −121 ppm °C, GFC of −114 ppm °C). At the same time, the water absorption of composites is decreased with an increase of the number of layers, which is almost twice that of other literatures (GFM of 0.019% and GFC of 0.005%). In consideration of low CTEx and CTEy of PTFE/GFC composites and low CTEz of PTFE/GFM composites, composite substrates with PTFE and alternate GFC and GFM were prepared, exhibiting relatively low CTE of 28.64, 30.52, 223.7 ppm C−1 at X, Y, Z directions, which is obviously superior to other substrates of the same type.